Automatic identification may be effected in different ways including many bar codes, identification tags and may be used to identify articles and personnel.
Radio Frequency Identification (RFID) is an automatic identification technology similar in application to bar code technology, but uses radio frequency instead of optical signals. An RFID system consists of two major components—a reader and a tag or card. They work together to provide the end user with a non-contact solution to uniquely identify people, animals or objects. The reader performs several functions, one of which is to produce a low-level radio frequency magnetic field that serves as a “carrier” of power from the reader to the RFID tag.
A passive RFID tag contains an antenna and an integrated circuit (IC). The IC requires only a minimal amount of electrical power to function. The antenna in the tag provides a means for gathering the energy present in the magnetic field produced by the reader, and converts it to an electrical signal for use by the IC. When a tag is brought into the magnetic field produced by the reader, the recovered energy powers the IC, and an electromagnetic signal modulated with data in the memory is transmitted by the tag's antenna. The electromagnetic signal transmitted from the tag is recovered by an antenna within the reader, and converted back into an electrical form. The reader contains a sensitive receiving system that is designed to detect and process the weak tag signal, demodulating the original data stored in the tag memory.
As opposed to passive tags, active tags contain a miniature battery that provides the operating power for the IC. When interrogated by the reader, the IC broadcasts a signal that identifies itself to sensitive reader detection and data transmission circuits. This allows the tag to begin sending its data at a considerably greater distance from the reader than its passive counterpart. Additionally, an active tag uses battery energy to produce a much stronger electromagnetic response signal. All of this results in a significantly greater read range than a passive tag.
Many present and upcoming applications require the ability to automatically identify objects from a distance. RFID provides this requirement to some degree and has the benefit that line-of-sight between the reader and tag is not required. This is distinct from optical recognition techniques, such as barcode, that require the optical reader to be in line of sight from the identified object. Most optical reading techniques also require a directional decoding of the identifying code, giving rise to start and stop bits being part of the code. In a conventional, linear bar code, the order in which the bars appear is critical and changing the order results in a different code. The same is applicable also to RFID tags, where typically reflectors in the tag are used to modulate the RF signal, such that the presence or absence of reflectors affects the resulting code that is returned by the tag.
U.S. Pat. No. 5,381,137 (“RF tagging system and RF tags and method”, assigned to Motorola, Inc., Schaumburg, Ill., published on 1995) discloses an RF tagging system that has a plurality of resonant circuits on a tag. When the tag enters a detection zone, the system determines the resonant frequency of each of the resonant circuits and produces a corresponding code. Resonant frequency detection is implemented by simultaneously radiating signals at each of the possible resonant frequencies for the tag circuits. The system is useful for coding any articles such as baggage or production inventory.
The reader in U.S. Pat. No. 5,381,137 comprises an antenna array having a plurality of fixed location multiple transmitter frequency probes. Tags comprise a plurality of passive resonant circuits, each of which may resonate at any different frequency selected from a predetermined plurality of known resonant frequencies. Each of the resonant circuits is fixed at a different location on a planar surface of the tag. The tag is positioned between guide rails so as to fix its position with respect to the plurality of fixed location probes. Either the tag is moved such that various rows of tuned circuits pass directly under the probes, or the probes are otherwise positioned directly above and in registration with the tuned circuits. By such means, each of the probes simultaneously radiates each of the possible resonant frequency signals which may correspond to the resonant frequency of any of the circuits.
Such a system is shown schematically in FIG. 1, showing a tag 10 that is encoded with multiple frequency sources to generate a code that is identified by a reader 11. Thus, as shown, the tag 10 comprises only three different frequency sources, depicted respectively f1, f2 and f3. It is seen that each of these frequency sources may be used more than once, its presence in, or absence from, the tag being depicted by “Y” and “N”, respectively. This does not cause any ambiguity since the frequency sources are spatially separated and the reader 11 is adapted to read each frequency source (which may be ambiguous) in association with its location (which is always unique). Thus, when a frequency source transmits a signal to the reader 11, this indicates that the frequency source is present at a known location, and the corresponding location in the resulting code construed by the reader may be set to logic “1” (or to logic “0” if negative logic is used). Since the location of each frequency source must be unique, the resulting code is likewise unique even if one or more of the transmitted frequencies is identical.
It is also known to use magnetic resonance (MR) for identification. Such is the case, for example, in the field of Magnetic Resonance Imaging (MRI) or Nuclear Magnetic Resonance spectroscopy (NMR spectroscopy). Furthermore, it is possible to identify multiple resonant frequencies detected in parallel. For example, according to U.S. Pat. No. 5,341,099 (“Magnetic resonance imaging apparatus”, assigned to Kabushiki Kaisha Toshiba, published on 1994) data is produced from asymmetrical echo data, and an MR image is reconstructed from the data thus produced.
Non-resonant frequencies, such as acoustical signals, are also used in the art for encoding data. For example, U.S. Pat. No. 6,611,798 (“Perceptually improved encoding of acoustic signals”, assigned to Telefonaktiebolaget LM Ericsson, published 2003) discloses encoding an acoustic source signal such that a signal reconstructed from the encoded information has a perceptually high sound quality. The acoustic source signal is encoded into at least one basic coded signal that represents perceptually significant characteristics of the acoustic signal. The encoder can include at least one spectral smoothing unit which receives at least one of the signal components on which the basic coded signal is based and generates in response thereto a corresponding smoothed signal component.